This invention relates to a pressure indicator, more particularly to a tire pressure indicator which indicates tire pressure through color coding.
Tire pressure detectors or indicators are known in the art. FIG. 1A shows a typical example of a tire pressure indicator having a piston member with an elongated pole which protrudes out of a casing, the degree of its protrusion dependent upon the amount of pressure in the tire. FIG. 1B shows an electrically operated tire pressure indicator having a light bulb D which acts as a warning signal. The bulb D lights up when, due to insufficient pressure, the conducting member C of the piston member A comes into contact with the electric contact element E. In these first two examples, the piston member A moves according to the pressure inside the space enclosed by a top casing T threaded to a bottom casing M, which is mounted to the inflating valve of a tire. A main drawback of these two examples is possible leakage of air from the tire to the surroundings due to loose threading of the connection between the top casing T and the bottom casing M.
To solve this problem, the structure of the two casings have to be improved. FIG. 2A shows an improved tire pressure indicator presented co-pending U.S. Pat. Application No. 07/392,749. In this figure, when the top casing T1 is threaded to the bottom casing M1, the piston member A1 separates the enclosed space in such a way that the air coming in from the tire can not reach the threaded portion of the two casings, thus minimizing the possibility of air leakage. Rod P, having graduations of pressure on its surface, extends downward from the top casing T1. Pressure is indicated by looking through the transparent bottom casing M1 to the level of the bottom surface of the piston member A1.
Though the device of FIG. 2A presents a solution to the problem of air leakage, the device itself is not very practical. For one thing, one would have to look very closely at the marked rod in order to determine whether there is sufficient pressure. This drawback is illustrated in FIG. 2B. Most people are not concerned with the actual value of the pressure in the tire, but rather with whether the pressure in the tire is sufficient.
Another main drawback of the prior art disclosed is that none provides for an automatic corrective means should the pressure in the tire be in excess of the required amount.